Improvements in or relating to networks

ABSTRACT

A network comprising a plurality of nodes ( 10 - 17 ) interconnected by communication links ( 20 - 27 ), wherein the nodes comprise pairs of nodes ( 10, 17 ) configured as maintenance end points. Each maintenance end point of each pair is configured to transmit continuity check messages to the other maintenance end point of the pair. Each maintenance end point is arranged to transmit a continuity check message according to a schedule such that an impact of transmission of the continuity check message on the network resources is reduced.

TECHNICAL FIELD

This invention concerns improvements in or relating to networks and inparticular, but not exclusively, to optical networks using Ethernet, inparticular OAM (Operation, Administration, Maintenance) enabled Ethernetand more particularly, in accordance with the ITU Y.1731 Ethoamstandard.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of an embodiment of a network inaccordance with the invention;

FIG. 2 is a diagrammatic view of an embodiment of a maintenance endpoint in accordance with the invention;

FIG. 3 is a timeline of two schedules in accordance with the invention;

FIG. 4 is a flowchart showing a method in accordance with an embodimentof the invention; and

FIG. 5 is a flowchart showing a method in accordance with an embodimentof another aspect of the invention.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, a network according to an embodiment of theinvention comprises a plurality of nodes 10 to 17 interconnected bycommunication links 20 to 28, such as fibre optic cables. The networkuses Ethernet, in particular OAM (Operation, Administration,Maintenance) enabled Ethernet in accordance with the ITU Y.1731 Ethoamstandard.

The plurality of nodes 10 to 17 comprise pairs of nodes 10 and 17, 11and 12, 13 and 14 and 15 and 16 configured as maintenance end points(MEPs). Each MEP 10 to 17 of each pair transmits continuity checkmessages (CCMs) to the other MEP 10 to 17 of the pair. The CCMs arededicated messages used for checking that the network is working, forexample, each MEP 10 to 17 may be able to determine faults in thenetwork as a result of the absence of an expected CCM or from datacontained in the CCM.

The network may be divided into sections 1 to 4 of the network (asindicated by the dotted lines) and each section 1 to 4 may becontrolled/maintained by different operators. Each section 1 to 4 of thenetwork may comprise one or more pairs of MEPs that the operator can useto determine whether that section 1 to 4 of the network is operating asit should be. In some instances, one operator may have somecontrol/maintenance responsibilities over a section of the network thatencompass other sections of the network controlled/maintained by otheroperators (in this instance section 1 includes sections 2 to 4). MEPsthat operate for sections of the network that encompass other sectionshaving dedicated MEPs are said to operate on a higher level and the CCMssent by MEPs of the higher level sections pass through MEPs of lowerlevel sections. For example, CCMs sent by MEPs 10, 17 pass through MEPs11 to 16. The operator of higher level section 1 considers MEPs 11 to 16to be maintenance intermediate points (MIPs). MIPs 11 to 16 do notinitiate CCMs that are sent to MEPs 10, 17 that operate on a higherlevel but can listen to the higher level CCMs that pass therethrough.

Referring to FIG. 2, each MEP 10 to 17 comprises a processor 50 andmemory 51 and can be programmed (configured) to operate as desired.

The network may also comprise a management system 30 for configuring andcontrolling the MEPs 10 to 17. In this embodiment, the management system30 is shown as a single device and communicates with the MEPs along thecommunication links 40 and 20 to 28. It will be understood however thatthe management system may comprise more than one device and maycommunicate with the MEPs over a dedicated communication link.

In accordance with the invention, each MEP 10 to 17 is arranged totransmit a CCM in accordance with a schedule such that an impact oftransmission of the CCMs on network resources is reduced. In particular,to reduce network traffic at any one instant as a result of thetransmission of CCMs, each MEP 10 to 17 is configured to transmit a CCMat a different time to the transmission of a CCM by another of the MEPs10 to 17. Ideally, the transmission of CCMs by the MEPs 10 to 17 shouldbe scheduled such that, as far as possible, the times of transmission ofCCMs by the MEPs 10 to 17 are evenly distributed.

FIG. 3 illustrates two examples of schedules for the transmission ofCCMs in accordance with the invention. The first example is for anetwork comprising two pairs of MEPs, 1 and 2. The transmission of a CCMby either one of the MEPs of pair 1 is indicated by MEP 1 and thetransmission of a CCM by either one of the MEPs of pair 2 is indicatedby MEP2. The top line indicates transmission of a CCM by an MEP of thepair in one direction in the network (from left to right or right toleft in the network as shown in FIG. 1) and the bottom line indicatestransmission of a CCM by the other MEP of the pair in the otherdirection. As can be seen, the MEPs are configured to transmit the CCMsin a sequence that is repeated cyclically such no one transmission of aCCM coincides with another. In this way, traffic at any instant due totransmission of CCMs is reduced.

The second example of a schedule according to the invention indicatesscheduling wherein it is not possible to have a unique transmission timefor each CCM. In this case, any two MEPs may transmit CCMs at the sametime. In this way, the instantaneous traffic due to CCMs is kept to aminimum.

It will be understood that the above embodiment is for illustrativepurposes only and in most practical situations, a network will comprisemany more pairs of MEPs and the transmission time (time slice) for a CCMis likely to be much shorter. For example, in one embodiment, the cyclicperiod is of the order of milliseconds and is divided into a hundred ormore time slices. In one embodiment, the cyclic period is 2 ms and isdivided into 500 time slices.

The schedule for the MEPs may be determined and/or managed by themanagement system 30. The management system 30 may be programmed todetermine the schedule for the transmission of CCMs by the MEPs 10 to 17and configure the MEPs 10 to 17 in accordance with this determination.This method carried out by the management system is illustrated in FIG.4.

Determining the schedule may comprise dividing a cyclic period, duringwhich a sequence of CCMs are to be transmitted, into a set number oftime slices, and allocating one of these time slices to the transmissionof CCMs by a specified one of the MEPs 10 to 17 such that thetransmission of CCMs is distributed, preferably as evenly as possible,across the cyclic period.

It will be understood that other methods of scheduling may be used inaccordance with the invention such that transmission of CCMs isdistributed across a cyclic period (rather than transmission of all CCMsin one cycle simultaneously).

In one embodiment, each CCM comprises sent count data on the number ofdata frames that have been sent from the MEP to the corresponding MEP ofthe pair, received count data on the number of data frames received bythe MEP from the corresponding MEP of the pair and a copy of sent countdata contained in the last CCM received by the MEP from thecorresponding MEP of the pair.

The MEPs can use such information to calculate data frame loss. However,if a CCM message itself fails to be transmitted, this can result in thedata frame loss calculated from the data contained in later receivedCCMs to be incorrect. In particular, the MEPs are programmed to includein a transmitted CCM a copy of sent count data contained in the last CCMreceived by the MEP from the corresponding MEP of the pair. In the priorart networks, an MEP has no way of knowing from the copy of sent countdata contained in a received CCM whether one of its sent CCMs was lost.Therefore, the MEP has no way of knowing that the received count datadoes not tally with the copy of sent count data contained in a receivedCCM when one of its sent CCMs has been lost. Consequentially, data frameloss calculations based on such data in the received CCM may bepresented as valid even though it is incorrect.

In accordance with one aspect of the invention, each MEP may beprogrammed to carry out the method shown in FIG. 5. In this method, eachMEP is arranged to store in memory the sent count data contained in CCMstransmitted from the MEP and compare the stored sent count data to thecopy of sent count data contained in CCMs received from thecorresponding MEP of the pair to determine if a CCM was lost. Forexample, if there is no corresponding value of sent count data in memoryto the copy of sent count data contained in the received CCM then theMEP can assume that a CCM has been lost.

In order to provide efficient processing, each MEP may be arranged tosearch through the stored sent count data from oldest to newest to findthe oldest stored sent count data with a value equal to a value of thecopy of sent count data contained in a CCM received from thecorresponding MEP of the pair and that is not older than any invalidatedstored count data. If such a value if found then that data entry isinvalidated (marked found). However, if no entry is found before aninvalidated entry, then the MEP determines that a CCM has been lost andinitiates appropriate action. For example, the MEP may be programmed togenerate a signal indicating that any data frame loss calculation basedon data contained in that CCM is invalid.

1.-27. (canceled)
 28. A network, comprising: a plurality of nodesinterconnected by communication links, the plurality of nodes comprisingpairs of nodes configured as maintenance end points (MEPs), wherein eachMEP of each pair is configured to transmit continuity check messages(CCMs) to the other MEP of the pair, and each MEP is arranged totransmit a CCM in accordance with a schedule such that an impact oftransmission of CCMs on network resources is reduced.
 29. The network ofclaim 28, wherein each MEP is arranged to transmit a CCM at a timedifferent from a time of transmission of a CCM by another of the MEPs.30. The network of claim 29, wherein a cyclic period during which asequence of CCMs is transmitted is divided into a set number of timeslices, and each MEP is arranged to transmit a CCM during one of thetime slices such that transmissions of CCMs by the plurality of MEPs aredistributed across the cyclic period.
 31. The network of claim 30,wherein each MEP is arranged to transmit a CCM during one of the timeslices such that transmissions of CCMs by the plurality of MEPs aresubstantially evenly distributed across the cyclic period.
 32. Thenetwork of claim 30, wherein the cyclic period is of the order ofmilliseconds (ms) and is divided into at least one hundred time slices.33. The network of claim 32, wherein the cyclic period is two ms and isdivided into 500 time slices.
 34. A method of configuring a network thatincludes a plurality of nodes interconnected by communication links, theplurality of nodes including pairs of nodes configured as maintenanceend points (MEPs), and each MEP of each pair being configured totransmit continuity check messages (CCMs) to the other MEP of the pair,the method comprising configuring each MEP to transmit a CCM inaccordance with a schedule such that an impact of transmission of theCCMs on network resources is reduced.
 35. The method of claim 34,wherein each MEP is configured to transmit a CCM at a time differentfrom a time of transmission of a CCM by another of the MEPs.
 36. Themethod of claim 35, wherein a cyclic period during which a sequence ofCCMs is transmitted is divided into a set number of time slices, andeach MEP is configured to transmit a CCM during one of the time slicessuch that transmissions of CCMs by the plurality of MEPs are distributedacross the cyclic period.
 37. The method of claim 36, wherein each MEPis configured to transmit a CCM during one of the time slices such thattransmissions of CCMs by the plurality of MEPs are substantially evenlydistributed across the cyclic period.
 38. The method of claim 36,wherein the cyclic period is of the order of milliseconds (ms) and isdivided into at least one hundred time slices.
 39. The method of claim38, wherein the cyclic period is two ms and is divided into 500 timeslices.
 40. A method of determining a time at which maintenance endpoints (MEPs) of a network transmit continuity check messages (CCMs),comprising: dividing a prescribed time period into a set number of timeslices; and sequentially allocating time slices to transmissions of CCMsby MEPs until all MEPs have been allocated a time for transmission of aCCM; wherein each MEP is allocated a different time for transmission ofa CCM unless all time slices have been allocated, whereupon more thanone transmission of a CCM by a MEP is allocated to each time slice. 41.A management system for a network having a plurality of nodesinterconnected by communication links, the plurality of nodes includingpairs of nodes configured as maintenance end points (MEPs) that transmitcontinuity check messages (CCMs) to each other, wherein the managementsystem, when connected in the network, is arranged to control each MEPto transmit a CCM in accordance with a schedule such that an impact oftransmission of the CCMs on network resources is reduced.
 42. Anon-transitory computer-readable medium having stored instructions that,when executed by a computer in a network having a plurality of nodesinterconnected by communication links, the plurality of nodes includingpairs of nodes configured as maintenance end points (MEPs) that transmitcontinuity check messages (CCMs) to each other, cause each MEP totransmit a CCM in accordance with a schedule such that an impact oftransmission of the CCMs on network resources is reduced
 43. A networknode for a network having a plurality of nodes interconnected bycommunication links, the plurality of nodes including pairs of nodesconfigured as maintenance end points, the network node comprising aprocessor and a memory configured to work as a maintenance end pointpair-wise with a second maintenance end point and to transmit continuitycheck messages to the second maintenance end point, wherein the networknode is arranged to transmit the continuity check messages in accordancewith a schedule such that an impact of transmission of the continuitycheck messages on network resources is reduced.
 44. A network,comprising: a plurality of nodes interconnected by communication links,the plurality of nodes comprising pairs of nodes configured asmaintenance end points (MEPs) that transmit continuity check messages(CCMs) to each other, each CCM comprising sent count data on a number ofdata frames that have been sent from a MEP to the other MEP of the pair,received count data on a number of data frames received by the MEP fromthe other MEP of the pair, and a copy of sent count data contained in alast CCM received by the MEP from the other MEP of the pair, whereineach MEP is arranged to store in memory the sent count data and tocompare stored sent count data to the copy of sent count data containedin CCMs received from the other MEP of the pair to determine if a CCMwas lost.
 45. The network of claim 44, wherein each MEP is arranged toinvalidate stored sent count data when a CCM is received from the otherMEP of the pair that contains a copy of sent count data that is equal invalue to the stored sent count data.
 46. The network of claim 45,wherein each MEP is arranged to search through stored sent count datafrom oldest to newest to find oldest stored sent count data with a valueequal to a value of the copy of sent count data contained in a CCMreceived from the other MEP of the pair and to invalidate that storedsent count data and any older stored sent count data.
 47. The network ofclaim 45, wherein each MEP is arranged to search through stored sentcount data from newest to oldest until either an invalidated stored sentcount data or oldest stored sent count data with a value equal to avalue of the copy of sent count data contained in a CCM received fromthe other MEP of the pair is found, and to invalidate the oldest storedsent count data if oldest stored sent count data with a value equal to avalue of the copy of sent count data contained in a CCM received fromthe other MEP of the pair is found.
 48. The network of claim 44, whereinin response to determination that a CCM was lost, the MEP generates asignal indicating that a data frame loss calculation based on datacontained in the CCM lost is invalid.
 49. A maintenance end point (MEP)for a network having a plurality of nodes interconnected bycommunication links, the plurality of nodes comprising pairs of nodesconfigured as MEPs that transmit continuity check messages (CCMs) toeach other, each CCM including sent count data on a number of dataframes that have been sent from a MEP to the other MEP of the pair,received count data on a number of data frames received by the MEP fromthe other MEP of the pair, and a copy of sent count data contained in alast CCM received by the MEP from the other MEP of the pair, whereineach MEP is arranged to store in memory the sent count data and tocompare stored sent count data to the copy of sent count data containedin a CCM received from the other MEP of the pair to determine if a CCMwas lost.